This description relates to an apparatus and method for sensing load of an electric cooker.
In general, a cooker generates heat by using an electric heater or by burning fuels such as liquefied petroleum gas (LPG) or liquefied natural gas (LNG). Further, a cooking vessel is heated by the generated heat to thereby cook a predetermined type of food.
Although there are many kinds of cookers, an electric cooker capable of generating heat using electricity and cooking food thereby is very convenient and thus tends to be widely used.
In particular, studies on high output and high efficiency induction heating used as a major heat source of an electric cooker such as a hob or a cook top have been actively conducted.
An induction heating electric cooker supplies a high frequency electric current to an induction heating coil to generate high frequency magnetic flux. The high frequency magnetic flux is induced into a cooking vessel placed on the top of a heater unit by an induction effect to generate an eddy current in the cooking vessel. Joule heat is generated in a resistance portion of the cooking vessel by the generated eddy current. The cooking vessel is heated by the generated Joule heat.
Such an induction heating electric cooker has an advantage of excellent heating efficiency in a cooking vessel over an electric cooker using an electric heater.
However only a cooking vessel made of a magnetic substance containing iron ingredients can be used for Joule heat to be generated in the resistance portion of the cocking vessel by the eddy current. In other words, a cooking vessel made of a non-magnetic substance such as ceramics, glass or porcelain cannot be employed because the Joule heat is not generated therein.
Studies for overcoming such limitations in an induction heating electric cooker have been actively conducted. As a result, an induction heating electric cooker capable of heating not only a cooking vessel made of a magnetic substance containing iron ingredients but that of a non-magnetic substance such as copper or aluminum has been developed.
The cooking vessel made of a non-magnetic substance has a lower permeability than that of the cocking vessel made of a magnetic substance. Therefore, a heated cooking vessel made of a non-magnetic substance would increase an operation frequency, or the number of windings of an induction heating coil and a current.
However, an induction heating coil of an electric cooker capable of heating the cooking vessels made of magnetic and non-magnetic substances alike has a complicated structure as compared with that of the electric cooker capable of heating only the cooking vessel made of a magnetic substance. Further, in the electric cooker capable of heating the cooking vessels made of magnetic and non-magnetic substances, an inverter for supplying high frequency current to the induction heating coil has a complicated structure to increase subsequent economic costs.
Furthermore, the heating efficiency, when a cocking vessel made of a non-magnetic substance is heated, is remarkably lower than that of a heated cooking vessel made of a magnetic container. That is, the heating efficiency of an electric cooker for heating a cooking vessel made of a non-magnetic substance is lower than that of an electric cooker for heating a cooking vessel using radiant energy generated by an electric heater.
The induction heating electric cooker can be used to heat a cooking vessel made of a metallic material, regardless of magnetic or non-magnetic, but cannot be used to heat a cooking vessel made of a non-metallic material such as ceramic, glass or porcelain.
The use of radiant energy for heating a cooking vessel is known in the prior art. For example, EP No. 1,049,358 discloses a cooking vessel heated by radiant heat generated by an electric heater. According to the technique, an electric heater for heating a cooking vessel is installed at a central portion of a heater unit, and a conductive sensor loop is installed at an outer periphery of the electric heater. Further, a signal with a certain frequency generated by an oscillation circuit produces frequency displacement in accordance with existence or non-existence of the cooking vessel and also generates a phase difference between voltage and current.
The conductive sensor loop detects a phase difference between the voltage and current of the signal with a certain frequency from which displacement is generated according to presence or absence of the cooking vessel, and compares the detected phase difference between the voltage and current with a predetermined reference value to determine the presence or absence of the cooking vessel. Accordingly, the conductive sensor loop can determine whether heat is generated by the electric heater based on a result of the determination.
Likewise, the aforementioned conventional technique can be employed to detect only the presence or absence of a cooking vessel made of metal, but cannot detect the presence or absence of a cooking vessel made of glass, ceramic, porcelain or the like. Further drawback is that since a cooking vessel is heated by an electric heater, the aforementioned technique has lower heating efficiency as compared with that of case where a cooking vessel made of a magnetic substance is heated by an induction heating electric cooker.
Meanwhile, inventors of the present invention have developed an electric cooker in which a single heater unit equipped with both an induction heater and an electric heater is provided so that the induction heater and the electric heater can be selectively operated to heat the cooking vessel according to the kind of a cooking vessel placed on the heater unit.
The electric cooker mounted with both the induction and electric heaters provided in a single heater unit can selectively operate the induction heater or electric heater by a user's manipulation of a function key according to the kind of a cooking vessel.
Where a user selectively operates the induction heater or the electric heater, the user should personally determine whether a cooking vessel is made of a magnetic or non-magnetic substance. Further, the user should manipulate a function key for operating the induction heater when the cooking vessel is made of a magnetic substance, whereas the user should manipulate a function key for operating the electric heater when the cooking vessel is made of a non-magnetic substance, which have caused troubles and inconveniences.
Accordingly, it is preferable to first determine presence or absence of a cooking vessel and the kind of the cocking vessel placed on a heater unit and to selectively operate an induction heater or an electric heater based on a result of the determination.